Telecommunication satellites usually comprise a platform and a payload, the latter being comprising all equipments, notably all devices intended for generating and transmitting high power radiofrequency signals—hereinafter referred to as RF signals—toward the ground. Different known techniques are resorted to for transmitting high power RF signals.
A first technique is based on the solid state technology, and involves Solid State Power Amplifiers, usually referred to as SSPAs. SSPAs notably have the drawback of not being in a position to manage usually requested levels of RF power.
A second technique is based on the use of Travelling Wave Tube Amplifiers, hereinafter referred to as TWTAs. TWTAs notably comprise a Travelling Wave Tube, hereinafter referred to as TWT. Telecommunication satellite payloads nowadays extensively use TWTAs. TWTAs are particularly efficient devices for high power RF transmission channels, and allow for managing very high levels of transmitted RF power. TWTA relies on a tube-based technology which requests a very precise tuning, not only on the manufacturing level, but also as regard to the accuracy of electrical interfaces. A TWT is described in much detail below in reference to FIG. 1, and basically comprises an RF input and an RF output, a helix, and electrodes comprising a cathode emitting electrons forming an electron beam, an anode, usually referred to as “Anode Zero” or “Anode 0”, focussing the electron beam, and a plurality of collectors. Usually, the cathode current is related to the Anode Zero voltage through a factor being usually referred to as “pushing factor”. It shall be observed that Anode Zero voltage is hereinafter referred to as the electrical potential difference between the Anode Zero electrode and the cathode. It shall be understood though, that a person of ordinary skill in the art may equally be able to carry out the invention by considering the Anode Zero voltage in reference to the helix electrical potential, or any other reference potential.
A TWTA usually comprises a TWT, associated with an Electronic Power Conditioner, hereinafter referred to as EPC, whose purpose is to supply the TWT with requested electrical operational conditions and to transfer the requested level of power from the electrical source to the TWT. The EPC is usually a DC-DC power converter supplied in energy through a primary bus, and generating the voltage levels requested on each of the electrodes comprised in the TWT, with an accuracy level allowing to ensure the TWT performances, that is: its linearity, the efficiency and the stability of the power transfer.
More specifically, there exist known TWTAs referred to as LTWTAs, standing for Linearized TWTAs, which further comprise an additional linearized preamplifier aiming at conditioning the RF signal level with the RF input of the TWT, and providing compensation to spurious nonlinearity phenomena notably brought by the TWT.
Dual TWTAs are specific TWTAs, essentially consisting of two TWTs driven by one EPC. The TWTs can then be used simultaneously and independently, or RF combined in order to provide higher power output RF signals. Therefore, a dual TWTA can be considered as an assembly of the following sub-functions:                two TWTs aiming at transferring the DC power to RF signal through 2 independent channels,        one EPC aiming at providing power supply and electrode polarization to both TWTs.        
Likewise, there exist dual LTWTAs, which are comprising the sub-functions described above, as well as two Linearized preamplifiers aiming at conditioning the RF signal for the respective inputs of both TWTs, and to provide compensation to the linearity errors thereof.
One major drawback of Dual TWTAs lies on the turn-on management of the second TWT: indeed, in order to avoid any defocusing of the TWT electron beam, high voltages shall be applied only when a certain cathode temperature is reached. An EPC for a dual TWTA therefore usually comprises means for managing the pre-heating phase of the cathode. Thus, at turning on of the second TWT, the channel passing through the first TWT is interrupted for the time the second TWT cathode reaches its operational temperature, which can be of the order of a few minutes. This phenomenon therefore implies a traffic interruption, which is in conflict with the operator's requirements in terms of satellite's channel operability.
One existing solution aiming at palliating the afore-mentioned drawbacks can be implemented in LTWTAs, and basically consists in turning on the second TWT very early during the satellite's mission and to letting it in a “no drive” operating mode for all the time it shall not be actually used in operation. The “no drive” operating mode may also be referred to as “RF mute” mode, and is managed through the linearized preamplifiers. “RF mute” mode is essentially a mode wherein no RF signal is conducted through the TWT. This solution shall penalize the satellite's payload, notably caused by useless power dissipation and related thermal management constraints. Indeed, as the unused second TWT is operated in no-drive mode, while the first TWT is being operated, the second TWT nevertheless continues consuming DC power and dissipating heat.
One other existing solution essentially consists of using the Power Flexibility functionality of the EPC, which essentially consists of adapting the TWT power by setting its optimum operating point, or saturation point, through adjusting the cathode current. Such solution allows setting the output power command to its minimum that is: typically attenuating it by 3 dB. This also allows reducing power but not yet to the extent proposed by the object of current invention.